My best guess is a third round TKO for St-Pierre, he'll tag Diaz with a ton of leg kicks and jabs with throws mixed in. By the middle of the third round the fight will be over St-Pierre will either catch Diaz with a vicious cross while standing or take him down beat a nearly blind (from the jabs) Diaz within inches of death before it's stopped. My second best guess is that St-Pierre will look to take Diaz down immediately and control with his wrestling, and he will succeed initially until sometime in the late second round Diaz catches him in a submission that no one has ever heard of before and pulls the upset.